The present invention relates to tough heat-formable sheet materials and articles made therefrom comprising a high-molecular weight synthetic resin as stiffening component. Such materials and articles are used, for example, in the shoe industry as counters; toe puffs and counters are preshaped elements, often in the form of a stiff fabric, coated with non-blocking, easy-heat or solvent-activatable adhesive. During shoe-making, these elements are softened, firstly so that they will conform to the required shape during the shoe-making operations and secondly to develop adhesive properties so that they can bond to the adjacent upper material. This bonding is achieved by a short solvent dip just prior to use, or by heat or by a combination of solvent and heat. Such materials have the disadvantages generally attributed to solvents, the pre-heating operation renders them sticky and hot and also they tend to stiffen rapidly on cooling.
To be useful as a counter material, a sheet material should be `tough`, that is, it should be resilient, flexible and non-cracking and preferably selfsupporting. Such materials are particularly suitable where resilience must be retained after adhesive bonding, as is the case in shoe making but also in applications such as garment labelling. Alternative stiffening materials/elements have been proposed where the stiffening material is the adhesive itself, covered by a light scrim to facilitate handling. Before moulding they are preheated to about 80.degree. C., the scrim being adequate to avoid adhesive penetration under light handling, so avoiding sticky handling. When in position, slight pressure and optional further heat application produces adhesive penetration through the scrim and wetting and bonding of the upper material.
Since the adhesive itself is also the stiffening material, its composition can be selected to adjust the change from the hot, malleable state to the stiff, crystalline state, so that the elements can remain malleable for several shoe operations.
Counters of this type have been produced using a very high molecular weight caprolactone polymer having a molecular weight of 50 000 (est). However, such materials suffer in turn from the fact that in practice such high molecular weight polymers can only be applied in powder form and then sintered.
In shoe making, temperatures above 100.degree. C. are avoided because of likely damage to materials and somewhat lower temperatures are therefore adopted for press operation and thus for softening materials for shaping purposes and for activating adhesives. Generally, temperatures in the range 60.degree.-125.degree. C., are adopted for these purposes, preferably 85.degree..+-.5.degree. C. Consequently, materials required for shoe counters must be relatively low-melting to suit the press requirement but this has to be associated with a high degree of stiffness/crystallinity to get the necessary toughness. This has hitherto been achieved by increasing molecular weight but this brings with it corresponding increases in viscosity.
It is accordingly an object of the present invention to provide a tough, heat-formable sheet material or articles made therefrom which can be more readily formed and processed by conventional shoe operation techniques.